Lubricating oil base stock production by hydrocracking two separate feed-stocks

ABSTRACT

A MULTIPLE-STAGE PROCESS FOR PRDUCING LUBRICATING OIL BASE STOCKS HAVING VISCOSITY INDICES GREATER THAN ABOUT 100. THE HEAVIER PORTION OF THE CHARGE STOCK, HAVING AN INITIAL BOILING POINT IN THE RANGE OF ABOUT 800*F. TO ABOUT 925* F. IS PROCESSED IN A FIRST STAGE; THE FRONT END OF THE RESULTING PRODUCT EFFUENT IS PROCESSED IN A SECOND STAGE, IN ADMIXTURE WITH THE LIGHTER PORTIONOF THE FRESH FEED CHARGE STOCK. A SERIES OF SEPARATION STEPS IS EMPLOYED TO RECOVER THE LUBRICATING OIL BASE STOCK WHILE CONCENTRATING A HIGH VISCOSITY INDEX BRIGHT STOCK.

Ma 1972 c. H. WATKINS LUBRICATING OIL BASE STOCK PRODUCTION BY HYDROCRACKING TWO SEPARATE FEEDSTOCKS Filed April 2, 1970 Rm Y Q 0m E T W N V a w T N n r t a 3 V 4 nmus x ni m e 6 m wmCmQ United States Patent LUBRICATING OIL BASE STOCK PRODUCTION BY HYDROCRACKING TWO SEPARATE FEED- STOCKS Charles H. Watkins, Arlington Heights, Ill., assignor to Universal Oil Products Company, Des Plaines, Ill.

Filed Apr. 2, 1970, Ser. No. 25,067 Int. Cl. Cg 37/02 US. Cl. 20859 10 Claims ABSTRACT OF THE DISCLOSURE A multiple-stage process for producing lubricating oil base stocks having viscosity indices greater than about 100. The heavier portion of the charge stock, having an initial boiling point in the range of about 800 F. to about 925 F. is processed in a first stage; the front end of the resulting product efiiuent is processed in a second stage, in admixture with the lighter portion of the fresh feed charge stock. A series of separation steps is employed to recover the lubricating oil base stock while concentrating a high viscosity index bright stock.

APPLICABILITY OF INVENTION The present invention involves the catalytic conversion of hydrocarbons in a multiple-stage process. More particularly, the present invention is directed toward the production of lubricating oil base stocks having viscosity indices above 100. A lubricating oil base stock is synonymously referred to in the art as a neutral oil, and is, in effect a dewaxed hydrocarbon mixture, boiling in the lubricating oil boiling range, which does not contain viscosity irnprovers or other additives. That is, a lubricatng oil denotes in the art a dewaxed product containing various additives. Through the utilization of the present invention, there is produced a waxy lubricating oil base stock having a viscosity index of above about 100. Following dewaxing, a standard prior art technique, the viscosity index remains above 100, and the resulting neutral oil is highly desirable for the production of multi-graded lubricating oils.

The prior art is replete with references to crude oils containing hydrocarbon components suitably adaptable for use as lubricating oils. In general, those lubricating oils derived from highly paraflinic crude stocks are utilized in the production of high quality motor oils, aviation oils and turbine oils. This type of lubricating oil is characterized by a relatively high viscosity index (V.I.), although, it actually is a blend of relatively low and relatively high viscosity index components. Lubricating oil base stocks which are derived from highly naphthenic crudes are employed in the production of lubricating oils having exceptionally desired properties with respect to a heavy duty use such as that found in diesel engines. Desirable components of lubricating oil base stocks, or neutral oils, are isoparaffins and molecules containing single rings, whether naphthenic or aromatic. However, essentially all heavy hydrocarbonaceous fractions, derived from crude oils, contain condensed-ring as well as straight-chain hydrocarbons. Characteristically, condensed-ring hydrocarbons have low viscosity indices and relatively poor resistance to oxidation. Therefore, they are undesirable as components of the various types of lubricating oils.

A perusal of the prior art procedures and techniques for producing lubricating oil base stocks indicates that relatively high viscosity index lubricating oils may be produced through the use of a combination of solvent extraction techniques and clay-treating, acid-treating, etc. Some heavy duty lubricating oils are obtained by way of vacuum distillation followed by alkali-treating for the re- 3,649,519 Patented Mar. 14, 1972 ice moval of naphthenic acids. The complex nature of high viscosity index lubricating oil production presents a challenge to the petroleum industry in the form of significant processing problems which are not easily solved through the use of present-day operating techniques. For example, solvent extraction of the undesirable components is ineflicient in view of the fact that the available solvents are not highly selective for the components which must be removed from the lubricating oil base stock. Furthermore, immense, complicated equipment is required for contacting the lubricating oil with the solvent and for the recovery of the solvent in order to make the process economically attractive. With respect to acid-treating and claytreating techniques, problems involve disposal of clay and loss of hydrocarbon yield, as well as an acidic sludge disposal problem when strong acids, such as sulfuric acid, are employed. By way of brief summation, it might be said that the prior art schemes are severely hampered in their capability to produce pure lubricating oils having high viscosity indices, and are tedious and expensive to operate in an acceptably efficient manner.

Candor compels recognition of the fact that certain prior art techniques are required if satisfactory lubricating oils are to be produced. Thus, it is necessary to subject a crude oil to one or more distillation techniques in order to provide a crude oil bottoms product concentrated in lubricating oil base stock. Another prior art scheme which may be required as a preliminary processing step, with respect to some crude oil bottom product, is a deasphalting process. The crude oil bottoms, containing asphaltenic constituents, is intimately admixed with a light hydrocarbon solvent such as propane, pentane or heptane, at conditions of temperature and pressure under which the asphaltenic constituents are precipitated. In view of the fact that the preliminary processing techniques of distillation and deasphalting are well known to those skilled in the art of petroleum refining technology, and form no essential part of my invention, further description thereof is not believed required herein.

Another prior art technique is necessary in order to produce a suitable lubricating oil base stock. Waxy constituents must be removed to improve the overall quality of the ultimate lubricating oil. The dewaxing technique is accomplished by a well known method which generally employs a solvent such as propane, methylethyl ketone, toluene, etc. The waxy lubricating oil base stock and solvent are heated to a temperature sufiiciently high to render the solvent and base stock substantially miscible. The resulting mixture is then chilled to precipitate the Wax from the solution. As hereinafter indicated, the dewaxing step adversely affects the viscosity index of the dewaxed product. Through the utilization of the present invention, a waxy lubricating oil base stock, having a viscosity index above is produced.

OBJECTS AND EMBODIMENTS A principal object of the present invention resides in the production of a maximum yield of lubricating oil base stocks. A corollary objective is to produce a dewaxed lube oil base stock pool having a fiat viscosity index profile. Viscosity Index Profile is herein defined as the change in viscosity index as a function of the viscosity of the lube oil cut taken from the entire lubricating oil base stock pool.

Another object of my invention is to produce lubricating oil base stocks, all of which have viscosity indices of about 100, from different fractions of a crude oil.

Before describing the various embodiments of the present invention, brief reference to the accompanying drawing will be made, in conjunction with the terms em ployed in the embodiments and appended claims, in

order that a clear understanding of the invention is made available. Therefore, referring briefly to the drawing:

(1) The first hydrocarbon charge stock is the deresined oil entering the process by way of line 1.

(2) First hydrocracking reaction zone is reactor 6.

(3) The second, lower-boiling hydrocarbon charge stock" is the waxy distillate being introduced by way of line 13.

(4) The second hydrocracking reaction zone is reactor 12.

(5 The first separation zone is hot separator 8 which provides a first principally vaporous phase in line 9 and a first principally liquid phase in line 10.

(6) The second separation zone is cold separator 17 which provides a second vaporous phase in line 2 and a second principally liquid phase in line 18.

(7) The third separation zone is hot flash chamber 11 providing a third principally vaporous phase in line 30 and a third liquid phase in line 19.

(8) The fourth separation zone is fractionator 20 which provides a fourth principally vaporous phase in line 22 and a high viscosity index bright stock in line 21.

(9) The fifth separation zone is cold flash chamber 23 which provides a fifth vaporous phase in line 24 and a fifth liquid phase in line 25.

(10) The sixth separation zone is fractionator 26 which provides the recovery of the waxy lubricating oil base stock in line 27.

In achieving the foregoing objects, my invention provides a process for producing a lubricating oil base stock which comprises the steps of: (a) reacting a first hydrocarbon charge stock and hydrogen in a first hydrocracking reaction zone, at hydrocracking conditions, in contact with a first hydrocracking catalyst; (b) separating the resulting first zone efiluent, at substantially the same pressure and at a temperature in the range of about 550 F. to about 825 F., in a first separation zone, to provide a first principally vaporous phase and a first principally liquid phase; (c) reacting said first vaporous phase and a second, lower-boiling hydrocarbon charge stock in a second hydrocracking reaction zone, at hydrocracking conditions, and in contact with a second hydrocracking catalyst; (d) separating the resulting second zone effluent at substantially the same pressure and at a temperature in the range of about 60 F. to about 140 F., in a second separation zone, to provide a second principally vaporous phase and second principally liquid phase; (e) recycling at least a portion of said second vaporous phase to combine with said first hydrocarbon charge stock; and, (f)

separating said first and second liquid phases to recover said lubricating oil base stock.

In another embodiment, said first and second liquid phases are separated to recover the lubricating oil base stock by the steps of: (a) separating said first liquid phase in a third separation zone, at substantially the same temperature and a reduced pressure, to provide a third vaporous phase and a third liquid phase; (b) separating said third liquid phase in a fourth separation zone, to provide a fourth vaporous phase and a fourth liquid phase; (c) separating said second liquid phase, and third vaporous phase and said fourth vaporous phase in a fifth separation zone, at substantially the same temperature and reduced pressure, to provide a fifth liquid phase and a fifth vaporous phase; and, (d) separating said fifth liquid phase in a sixth separation zone to recover said lubricating oil base stock.

Other objects and embodiments of my invention involve particularly preferred operating conditions and techniques, as well as preferred catalytic composites for utilization in the hydrocracking reaction zones. One Such embodiment relates to lower-severity operating conditions within the second hydrocracking reaction zone. Particularly included are a lower maximum catalyst bed temperature, a higher liquid hourly space velocity, or

both. Another such embodiment involves a first hydro- .4 carbon charge stock having an initial boiling point in the range of about 800 F. to about 925 F., while the second hydrocarbon charge stock has an initial boiling point above about 600 F. These, as well as objects and embodiments of my invention, will become evident from the following more detailed summary of the present lubricating oil base stock producing process.

SUMMARY OF INVENTION The hydrocarbon charge stocks, suitable for use in the present process, are conventional and well known in petroleum refining technology. Thus, suitable charge stocks include vacuum gas oils, propane deasphalted oils, reduced crude stocks, mixtures thereof etc. One illustrative feed stock is a mixture of 44.5 vol. percent of a raw waxy neutral oil, 23.6 vol. percent heavy vacuum gas oil and 31.9 vol. percent deasphalted oil. This particular charge stock indicates a gravity of about 24.4 API., and initial boiling point of 640 F., a 50.0% volumetric distillation temperature of about 899 F. and an end boiling point of about 1106 F. This feed stock is contaminated with undesirable materials as indicated by the presence of about 0.42% by weight of sulfur and 1,300 ppm. by weight of nitrogen. Another typical charge stock is a topped vacuum gas oil, derived from an Illinois crude, having a gravity of 22.3" APL, an initial boiling point of about 750 F., a 50.0% volumetric distillation temperature of 905 F. and end boiling point of about 1050 F. The vacuum gas oil contains about 1,630 ppm. by weight of nitrogen and 0.44% by weight of sulfur.

The multiple-stage process of the present invention is a catalytic process wherein the catalytic composites are disposed as fixed-beds in the various hydrocracking reaction zones. Although the precise composition of the cata lyst need not necessarily be identical in all stages, the catalytically active components of the various composites are generally selected from the metals of Groups VI-B and VIII of the Periodic Table. These metallic components are composited with a porous carrier material, and, in many applications, the catalytic composites will also contain a halogen component, generally from the group of chlorine, fluorine and mixtures thereof. Of necessity, the porous carrier material is refractory with respect to the operating conditions employed in the hydrocracking reaction zones, and it is intended to include those carrier materials which have traditionally been utilized to effect the hydrocracking of hydrocarbonaceous material. In particular, suitable carrier materials are selected from the group of amorphous refractory inorganic oxides including alumina, silica, titania, zirconia, magnesia, aluminasilica, silica-magnesia, alumina-silica-boron phosphate, silica-zirconia, etc. When of the amorphous type, one preferred carrier material constitutes a composite of alumina and silica, the silica being present in an amount of about 10.0% to about 90.0% by weight. The carrier material may consist of a crystalline aluminosilicate, and may be naturally-occurring or synthetically-prepared, including mordenite, fauiasite, Type A or Type B molecular sieves, etc. When utilized as the carrier, the zeolitic material may be in the hydrogen form or in a form which results from treatment with multivalent cations. No particular refractory inorganic oxide carrier material is essential to the present invention, and it is intended to include within the scope of the present invention all conventional carrier materials, as well as the wide variety of methods for the preparation thereof.

Preferred catalytic composites contain at least one metallic component from the metals of Groups VI-B and VIII as indicated in the Periodic Table of the Elements, E. H. Sargent and Company, 1964, although it is understood that the equivalent results are not achieved through the indiscriminant selection of metallic components. That is to say, a mixture of chromium and cobalt components will not yield results which are equivalent to those obtained through the use of molybdenum and nickel compo nents. Suitable metallic components include chromium molybdenum, tungsten, iron, nickel and cobalt, as well as the noble metals of Group VIII, ruthenium, rhodium, palladium, osmium, iridium and platinum. The Group VIII noble metal components generally comprise about 0.01% to about 2.0% by weight of the final composite, calculated on an elemental basis. The noble metal components may be incorporated within the catalytic composites in any suitable manner including co-precipitation or cogellation, ion-exchange or impregnation. When utilized as a component of the catalytic composite, the metals of Group VI-B, chromium, molybdenum and tungsten are utilized in an amount of from about 4.0% to about 30.0% by weight. The iron group metal components, iron, cobalt and nickel will be employed in an amount within the range of about 1.0% to about 10.0% by weight. These metallic components may also be composited with the carrier material in any suitable manner described within the prior art.

The hydrocracking process of the present invention eliminates the necessity for an initial extraction operation; however, as hereinbefore set forth, a final dewaxing technique is practiced in order to prepare a suitable lubricating oil base stock. While solvent extraction removes those components having a low viscosity index without chemical reactions being effected, hydrocracking simultaneously converts the components of low viscosity index into high quality naphthas and distillates, while converting the components of high viscosity index to a lesser extent, whereby the same continue to be within the boiling range of lubricating oils. During the hydrcracking of heavy distillates for the production of lubricating oil base stocks, the viscosity index profile, defined herein as being the viscosity indices of 10.0% by volume fractions of the total waxy lubricating oil, plotted as a function of volume percent distilled, indicates low viscosity indices at the front end, and higher viscosity indices on the heavier end. Thus, the viscosity index profile of the total waxy lubricating oil base stock pool typically indicates from about 10.0% to about 30.0% by volume, or more, as having a viscosity index below about 100. The viscosity indices of the remaining 10.0% fractions increases to values above 100, and often into the 130 to 140 range. It is very desirable to have the viscosity indices of all the dewaxed 10.0 vol. percent fractions above 100. In a specifically preferred lubricating oil base stock the initial 3 to 4 dewaxed 10.0% fractions each has a viscosity index of about 103 to 106. Were an attempt made to process the entire fresh feed charge stock at an operating severity such that the viscosity index of the front end is at least 105, the overall yield of lubricating oil base stock is decreased from about 5.0% to about 15.0% by volume, based upon fresh feed, and the viscosity index of the lighter oils is much higher than required. Another consideration involves the desired quality of the waxy lubricating oil base stock. In many instances, commercially-scaled units are designed to produce a waxy lubricating oil base stock having an intermediate viscosity index in the range of about 110 to 120. On the other hand, many other processes are effected in a manner which produces a waxy lubricating oil base stock having a viscosity index in the range of about 120 to about 145. The judicious selection of operating variables can so modify the present process that flexibility with respect to the viscosity index of the waxy lubricating oils is easily achieved.

In accordance with the present invention, the fresh feed charge stock is separated to provide a heavy bottoms, commonly referred to as a heavy cylinder stock, from which is derived the deresined oil hereinafter referred to. The initial boiling point of the cylinder stock, or the deresined oil, is in the range of about 800 F. to about 925 F. depending upon the character and quantity of the resins as well as that of the low viscosity index condensed-ring compounds. Another consideration is the quantity of asphaltenic compounds contained in the fresh feed charge stock. In a single-stage unit, the operating con ditions necessarily imposed upon the charge stock, in order to improve the viscosity index of the cylinder stock fraction, are such that excessive cracking of the lowerboiling portion is experienced. Although a single-stage unit will produce a lubricating oil base stock having an improved viscosity index, the volumetric yield thereof based upon the fresh feed charge stock is significantly decreased. The present scheme offers a modified series flow wherein the heavy cylinder stock fraction is processed separately from the lighter waxy distillate fraction. In the absence of the lighter material, the first stage can function acceptably at a higher severity with the result that a lesser quantity of lubricating oil components are converted into lower-boiling products such as naphtha and kerosene fractions, and the desired high viscosity base stocks (V.I.s above 100) are produced from the heavier material. The product effluent from the reaction zone, in which the deresined oil is processed, is separated in a hot separator at substantially the same pressure and a temperature in the range of about 550 F. to about 825 F., to provide a principally vaporous phase containing some hydrocar bons boiling above about 800 F. This front end frac tion is then combined with the lighter waxy distillate for processing in the second stage of the process. In the absence of the original heavier material, the second stage can function acceptably at the necessary operating severity with the result that the desired V.I is achieved. A series of separation techniques are utilized to concentrate and recover a high viscosity index bright stock separate from the waxy lubricating oil base stock product of the process. This permits back-blending of the bright stock with various neutral oils derived from the waxy lubricating oil base stock in order to produce intermediate V.I. lubricating oils. Where desired, the excess waxy bright stock may be recycled to combine with the deresined oil, with or without a diluent stream, in order to achieve additional cracking thereof into the lower-boiling lubricating oil components. The separation schemes are effected in a manner which generally produces a bright stock containing less than about 20.0% by volume of hydrocarbons boiling below about 900 F.

The hydrocarbon charge stock and hydrogen are contacted with a catalyst of the type hereinabove described in a hydrocracking reaction zone. The particular catalyst selected is primarily dependent upon the characteristics of the charge stock, as well as the desired end result. Although the catalytic composite may be the same in both hydrocracking reaction zones, many situations arise where enhanced results are achieved through the use of different catalytic composites. The contacting may be accomplished by using the catalyst in fixed-bed systems, moving-bed systems, fluidized-bed systems, or in batch-type operations. However, in view of the risk of attrition loss of the catalyst, it is preferred to use a fixed-bed system. Furthermore, it is well known that a fixed-bed catalytic system offers many operational advantages. In such a system, the reactants may be contacted with the catalyst in either upward, downward or radial flow fashion with a downward fiow being preferred. Additionally, the reactants may be in the liquid phase, a mixed liquid-vapor phase or a vapor phase when they contact the catalyst.

The specific operating conditions imposed upon the individual hydrocracking reaction zones are primarily dependent upon the physical and chemical characteristics of the fresh feed charge stock. However, with respect to the first hydrocracking reaction zone, wherein the heavier deresined oil is processed, the operating conditions will include a pressure from about 1,500 to about 3,000 p.s.i.g., an LHSV (liquid hourly space velocity) of about 0.3 to about 3.0, and a hydrogen concentration in the range of about 3,000 to about 15,000 scf./bbl. In view of the fact that the hydrocracking process is exothermic in nature, an increasing temperature gradient will be experienced as the hydrogen and feed stock traverse the catalyst bed. It is preferred that the maximum catalyst bed temperature in the first hydrocracking reaction zone, be main tained in the range of about 700 F. to about 900 F.

As hereinbefore stated, the product eftiuent from the first hydrocracking reaction zone is separated to provide a front end which is combined with the waxy distillate, the mixture being the charge to the second hydrocracking reaction zone. The second hydrocracking reaction zone is maintained at a lower operating severity than that which is imposed upon the first hydrocracking reaction zone. Its lower severity operation is achieved either by decreasing the maximum catalyst bed temperature, or increasing the liquid hourly space velocity, or through a combination of changes in both operating variables. Thus, although the hydrogen concentration and reaction zone pressure may be substantially the same, the maximum catalyst bed temperature will be in the lower range of about 600 F. to about 860 F., while the liquid hourly space velocity is in the range of about 0.5 to about 4.0. In order to assure that the catalyst bed temperature does not exceed the maximum allowed, conventional quench streams, either normally liquid or normally gaseous and introduced at one or more intermediate loci of the catalyst bed, may be utilized.

In the present specification and appended claims, a pressure substantially the same as or temperature substantially the same as, is intended to connote that the pressure or temperature under which a downstream vessel is maintained is the same, allowing only for the normal pressure drop due to fluid flow and the normal temperature loss due to transfer of materials from one zone to another. Thus, Where the first hydrocracking zone is at a pressure of about 2,650 p.s.i.g., and the temperature of the effluent may be as high as 875 F. the first separation zone will function at a pressure of about 2,550 p.s.i.g. and a temperature of about 50 F. lower. Similarly, although the second separation zone functions at substantially the same pressure the temperature of the second hydrocracking reaction effluent is decreased to a level of about 60 F. to about 140 F. The third separation zone and fifth separation zone, being a hot flash chamber and a cold flash chamber respectively, will function at a significantly reduced pressure in the range of about p.s.i.g. to about 300 p.s.i.g.

In further describing the process encompassed by my inventive concept, reference will be made to the accompanying drawing which illustrates one embodiment. For the purpose of demonstrating the illustrated embodiment, the drawing will be described in connection with a commercially-scaled unit having a fresh feed charge rate of about 4,500 barrels per day. It is understood that the charge stock, stream compositions, operating conditions, vessel designs, separators, catalysts and the like, are exemplary only, and may be varied widely without departure from my invention, the scope and spirit of which is defined by the appended claims.

DESCRIPTION OF DRAWING In the drawing, the embodiment is illustrated by means of a simplified flow diagram in which such details as pumps, instrumentation and controls, heat-exchange and heat-recovery circuits, start-up lines, compressor, valving and similar hardware have been omitted as not being essential to an understanding of the techniques involved. The utilization of such miscellaneous appurtenances, to modify the process, is well within the purview of one skilled in the art of petroleum refining techniques.

The fresh feed charge stocks are a waxy distillate and deresined oil derived from a full boiling range crude stock. The Waxy distillate constitutes about 28.3 vol. percent of the crude, while the cylinder stcok constitutes 16.6 vol. percent of which about 16.0% is the deresined oil. These charge stocks have the characteristics indicated in the following Table I:

Distillation, F.:

Initial boiling point 5.00%

End boiling point Sulfur, wt., percent Nitrogen, p.p.m Viscosity index *Dewaxed v.1. of about 98.

The intended object is to product maximum quantities of a lubricating oil neutral base stock and a bright stock base stock, both of which, upon dewaxing, indicate an overall viscosity index in the range of 100 to 105, or higher.

The deresined oil, in an amount of 1,640 barrels per day (31.51 mols/hr.) enters the process by way of line 1, being admixed with a hydrogen-rich recycle vaporous phase in line 2 in an amount of about 1,101.54 mols./hr. Make-up hydrogen, to supplant that consumed in the overall process and vented to fuel, is admixed with the recycle hydrogen stream in line 2 by way of line 3. Although not illustrated in the drawing, about 22467 mols/hr. of the circulating hydrogen is diverted to quench reactor 6 in order to maintain the increasing temperature differential at about 50 F. Following suitable heat-exchange to increase the temperature to about 600 F., the mixture enters heater 4, at a pressure of about 2,710 p.s.i.g., wherein the temperature is increased to a level of about 775 F. as measured at the inlet to the catalyst bed. The heated mixture passes through line 5 into reactor 6 at a pressure of about 2,680 p.s.i.g. The liquid hourly space velocity through the catalytic composite disposed in reactor 6 is about 0.5. Reactor 6 has disposed therein a fixed-bed of a catalytic composite of 1.8% by weight of nickel and 16.0% by weight of molybdenum, combined with an amorphous carrier material of 63.0% by weight of alumina and 37.0% by weight of silica. Component analyses of the charge to reactor 6 and the efiiuent being withdrawn therefrom by way of line 7 are presented in the following Table II, the values being given in mols/hr.

TABLE IL-REACTOR 6 STREAM ANALYSES The reactor efiiuent in line 7 is introduced into hot separator 8. In many instances, the temperature of the efliuent as it enters hot separator '8 is substantially the same as that at the outlet of reactor 6. Such a technique is generally practiced when it is desired to produce a lower yield of bright stock having a higher viscosity index than in the instant situation. In the present illustration, the hot eifiuent is utilized as a heat-exchange medium to lower its temperature to a level of about 600 F., prior to entering hot separator 3 at a pressure of about 2,625 p.s.i.g. A principally liquid phase is removed from hot separator 8 by way of line 10, and is introduced thereby into hot flash zone 11 at a temperature of about 595 F. and pressure about p.s.i.g. Hot flash zone 11 will normally function at pressure in the range of about 25 p.s.i.g. to about 300 p.s.i.g. The vaporous phase from hot separator '8, in line 9, is introduced into a second hydrocracking reaction zone 12. Component analyses of the etfluent streams from hot separator 8 are presented in the following Table III:

TABLE III.HOT SEPARATOR STREAM ANALYSES The waxy distillate, in an amount of 2,800 barrels per day (86.77 mols/hr.) is introduced into heater 14, and passes by way of line to combine with the first principally vaporous phase in line 9, the mixture continuing through the latter into reaction zone 12. Reaction zone 12 is maintained under a pressure of about 2,580 p.s.i.g., and a catalyst bed inlet temperature of about 725 F., the space velocity being about 1.0. The catalytic composite, disposed in reactor 12, is substantially identical to the nickel-molybdenum catalyst disposed within reaction zone 6. The reaction product eflluent is withdrawn at a temperature of about 775 F., by way of line 16, and is introduced therethrough, at a pressure of about 2,500 p.s.i.g. and a temperature of about 140 F., into cold separator 17.

Prior to being introduced into cold separator 17, the eflluent in line '16 is utilized at a heat-exchange medium whereby its temperature is decreased to the aforementioned level.

The analysis of the product eflluent from reactor 12 is presented in the following Table IV. The charge analysis is not indicated since it is merely composed of the hot separator vapor and the fresh feed waxy distillate.

TABLE IV.-REACT OR 12 ANALYSIS The separation elfected hot flash chamber 11 at a pressure of about 90 p.s.i.g. and a temperature of about 595 F. is indicated in the following Table V:

TABLE V.HOT FLASH STREAM ANALYSES Line 30 Line 19 C omponent:

Ammonia Hexane, 400 1. 400 F.-625 F 625 F., plus Fractionator is maintained under conditions of temperature and pressure such that the 625 F.-plus bright stock, removed therefrom in line 21, contains less than about 20.0 vol. percent of hydrocarbons boiling below about 900 F. Thus, of the material entering fractionator 20 by way of line 19, an overhead fraction comprising 625 F.-minus normally liquid hydrocarbons lubricating oil base stock and normally gaseous material, is removed by way of line 22. Cold separator 17 functions to provide a hydrogen-rich recycle gaseous stream in line 2, and a normally liquid stream in line 18. The cold separator liquid stream in line 18 is admixed with the hot fiash vapor in line 30 and the overhead from fractionator 20 in line 22, the mixture being introduced into cold flash zone 23 at a pressure of about p.s.i.g. and a temperature of about 135 F. Component stream analyses with respect to cold flash zone 23 are presented in the following Table VI:

TABLE VI.OOLD FLASH STREAM ANALYSES Line 24 Line 25 Component:

Ammonia Hydrogen sulfide. 0. 72 0. 21 Hydrogen 46. 01 0. 47 Methane 19. 64 1. 13 Ethane. 8.14 1. 80 Propane. 1. 93 1. 84 Butanes. 1. 49 2. 46 Pentanes. 0. 41 1. 66 Hexane, 400 0. 21 13. 69 400 F.-625 F 11. 13 625 F., plus 86. 50

With respect to cold flash zone 23, a principally vaporous phase is vented through line 24 to fuel, While a principally liquid phase in line 25 passes therethrough into fractionator 26. Fractionator 26 functions under conditions of temperature and pressure which produces a waxy lubricating oil base stock in line 27, a diesel or furnace fuel, boiling from about 400 F. to about 625 F., in line 28 and a naphtha boiling range fraction in line 29.

Pertinent product properties of the bright stock and lubricating oil base stock are presented in the following Table VII:

TABLE VIL-PRODUCI PROPERTIES Bright.

stock stock Gravity, API 29. 1 31. 6 Distillation, F.:

Initial boiling point- 625 625 5% 810 660 10% 850 680 30% 720 50% 775 70% 845 880 900 E nd boiling 920 Viscosity index 112 115 Viscosity index (dewaxed) 104 103 Molecular weight 620 410 In addition to the properties presented in the foregoing Table VII, sulfur and nitrogen analyses on both the bright stock and lubricating oil base stock indicate nil, or that the two products are substantially completely free from both nitrogenous and sulfurous compounds.

The foregoing specification, and particularly the illustration directed to a commercially-scaled unit, indicates the method by which the present invention is eifected and the benefits to be afforded through the utilization thereof.

I claim as my invention:

1. A process for producing a lubricating oil base stock which comprises the steps of:

(a) reacting a first hydrocarbon charge stock and hydrogen in a first hydrocracking reaction zone, at hydrocracking conditions, in contact with a first hydrocracking catalyst;

(b) separating the resulting first zone effluent, at substantially the same pressure and at a temperature in the range of about 550 F. to about 825 F., in a first 11 separation zone, to provide a first principally vaporous phase and a first principally liquid phase;

(0) reacting said first vaporous phase and a second, lower-boiling hydrocarbon charge stock in a second hydrocracking reaction zone, at hydrocracking conditions, and in contact with a second hydrocracking catalyst;

(d) separating the resulting second zone eflluent at substantially the same pressure and at a temperature in the range of about 60 F. to about 140 F, in a second separation zone, to provide a second principally vaporous phase and a second principally liquid phase;

(e) recycling at least a portion of said second vaporous phase to combine with said first hydrocarbon charge stock; and,

(f) separating said first and second liquid phases to recover said lubricating oil base stock.

2. The process of claim 1 further characterized in that said first hydrocarbon charge stock has an initial boiling point in the range of about 800 F. to about 925 F.

3. The process of claim 1 further characterized in that said second hydrocarbon charge has an initial boiling point above about 600 F.

4. The process of claim 1 further characterized in that the hydrocracking conditions, imposed upon said first hydrocracking reaction zone, include a maximum catalyst bed temperature of from about 700 F. to about 900 F. and a liquid hourly space velocity of from 0.3 to about 3.0.

5. The process of claim 1 further characterized in that the hydrocracking conditions imposed upon said second hydrocracking reaction zone include a higher liquid hourly space velocity in the range of 0.5 to about 4.0, a lower maximum catalyst temperature of from 600 F. to about 860 F., or a higher liquid hourly space velocity and a lower maximum catalyst bed temperature.

6. The process of claim 1 further characterized in that said first and second liquid phases are separated to recover said lubricating oil base stock by the steps of:

(a) separating said first liquid phase in a third separation zone, at substantially the same temperature and at a reduced pressure, to provide a third vaporous phase and a third liquid phase;

(b) separating said third liquid phase in a fourth separation zone, to provide a fourth vaporous phase and a fourth liquid phase;

(c) separating said second liquid phase, said third vaporous phase and said fourth vaporous phase in a fifth separation zone, at substantially the same temperature and a reduced pressure, to provide a fifth liquid phase and a fifth vaporous phase; and,

(d) separating said fifth liquid phase in a sixth separation zone to recover said lubricating oil base stock.

7. The process of claim 6 further characterized in that said third and fifth separation zones are maintained under a pressure of from 0 p.s.i.g. to about 300 p.s.i.g.

8. The process of claim 6 further characterized in that said sixth separation zone is maintain-ed at conditions of temperature and pressure selected maintain the initial boiling point of said lubricating oil base stock in the range of about 600 F. to about 700 F.

9. The process of claim 1 further characterized in that said first and second hydrocracking catalysts contain at least one metallic component from the metals of Groups VI-B and VIII combined with a porous carrier material.

10. The process of claim 6 further characterized in that said fourth separation zone is maintained at conditions of temperature and pressure selected to provide a fourth liquid phase of which less than about 20.0% by volume boils below a temperature of about 900 F.

References Cited UNITED STATES PATENTS 3,159,565 12/ 1964 Kimberlin et al. 208--78 3,321,395 5/1967 Paterson 208-78 3,544,448 12/1970 Jacobs et al. 20859 3,551,323 12/1970 Hamblin 20859 HERBERT LEVINE, Primary Examiner US. Cl. X.R. 

